Why Isn't Pterodactyl a Dinosaur?

Are Pterodactyls and other pterosaurs considered dinosaurs? There are flying dinosaurs, right? And what are dimetrodon and plesiosaurs? Paleontologist Danny Barta explains what a dinosaur is, and is not!

[A man stands in front of an orange background, talking to the camera.]

Danny Barta (PhD Candidate, Richard Gilder Graduate School, American Museum of Natural History): Many people think that pterosaurs are dinosaurs-

[On either side of Danny, white silhouettes of pterosaurs and dinosaurs appear with [POPPING NOISES]. A thought bubble emerges from his head and leads to the bottom of the screen where the text “Do Pterosaurs = Dinosaurs?” appears.]

because they’re reptiles and they lived at the same time as dinosaurs. But pterosaurs and dinosaurs-

[The equals sign is crossed out, so now the sentence reads “Pterosaurs DO NOT equal dinosaurs.”]

are not actually dinosaurs in the scientific sense.

[CAMERA CLICK]

[The video freezes on Danny smiling. A label appears next to him, reading “Danny Barta, Paleontologist”. The American Museum of Natural History logo appears over it. The screen swipes back to a close-up of Danny.]

So when we call something a dinosaur, we mean that it belongs to the group Dinosauria-

[A long-necked dinosaur appears with a tag around it’s neck that reads “Dinosaur”. Other dinosaurs appear and a bracket encloses them, with the label “Dinosauria”.]

-which was named by Sir Richard Owen in 1842.

[A teal screen pulls down, with a framed drawing of a man riding a fossil mammal. An arrow points to the man, reading “Sir Richard Owen”. An arrow points to the fossil, reading “(riding a fossil)”.]

And within Dinosauria there’s three main groups.

[The drawing disappears and the sides of the frame rotate to form a cladogram or evolutionary tree with three branches.]

You have the Ornithischian dinosaurs like Triceratops and Stegosaurus,

[A label of “Ornithischian” appears at the top of the leftmost branch. Silhouettes of a Triceratops and Stegasaurus swipe in from the left.]

and you have the long-necked Sauropod dinosaurs like Patagotitan and Apatosaurus,

[A label of “Sauropod” appears at the top of the center branch. Silhouettes of the bottom half of a titanosaur, Patagotitan, and an Apatosaurus fall from the top of the screen.]

and you also have the Theropod dinosaurs which includes the very famous Tyrannosaurus-

[A label of “Theropod” appears at the top of the rightmost branch. A silhouette of a T. rex swipes in from the right side of the screen.]

-as well as our birds that we see all around us today.

[The silhouette of a hawk and a chicken slide in around the T. rex. The screen slides back to Danny standing on an orange background.]

So when we think about biological classification, each group is nested within a larger group.

[Next to Danny’s head, a circle encloses the word “Dinosauria.”]

Dinosauria is nested within a larger group called Archosauria.

[The circle reduces to take up one portion of a larger circle, which is labeled “Archosauria”.]

Archosauria includes the close cousins of the dinosaurs – the pterosaurs that we talked about earlier –

[Two other circles appear within the larger Archosauria circle. One enlarges to show the label Pterosauria. Pterosaur silhouettes fly in the background.]

which includes todays crocodiles and alligators, as well as a number of extinct forms –

[A line of crocodiles and lizard-looking silhouettes parade through the circle.]

some of whom actually were dinosaur mimics.

[The parade stops on a spiny looking, dinosaur-like lizard. The circle zooms out to include a T.rex. Beneath the T. rex a checkmark appears next to the word “Dino” and under the crocodile ancestor, an X appears next to the word “Dino”.]

You may have even seen extinct crocodilians in a museum and thought they were dinosaurs, because they look so similar.

[Video footage of two crocodile ancestor fossils appears on screen. A circle encloses the face of one of them as it minimizes onto an evolutionary tree on the left. On the right side of the tree is a circle containing a T.rex fossil, and another circle containing a pterosaur fossil.]

Pterosaurs and dinosaurs are distinguished from all the crocodile line archosaurs

[The words “crocodile line” and “bird line” appear on the left and right sides of the evolutionary tree, respectively.]

Dinosaurs and pterosaurs separated from one another nearly 250 million years ago

[The circles containing the T.rex and pterosaur fossils separate and an evolutionary tree is drawn between them. At the stem of the tree, the label “250 million years” appears.]

on the basis of having a hole in their hip socket and a long crest on their upper arm bone.

[Under both the pterosaurs and the dinosaurs, two circles appear each: one with a drawing of the hip bones, and one with a drawing of the upper arm bone. For dinosaurs, there is a hole in the hip bones which is circled and labeled “hole”, and a thin line on the arm bone labeled “crest”. For pterosaurs, there is no hole in the hip bones, the same area of which is circled and labeled “no hole” and the arm bone is smooth and circled and labeled “no crest”.]

250 million years ago is really a long time geologically,

[Danny is back on screen again. Beneath him, a timeline rolls out from the present day back to 250 million years ago. A smaller timeline shows that 66 million years ago, “non-avian dinos + all pterosaurs die out”.]

so dinosaurs and pterosaurs, while they may be close cousins in an evolutionary sense

[The silhouette of a pterosaur and a duck-billed dinosaur appear on screen. A speech bubble appears over each, reading “ ‘sup”.]

are really quite widely separated.

[The dinosaur and the pterosaur silhouettes move away from each other to the opposite ends of the screen.]

Now there are flying dinosaurs;

[The pterosaur goes back to the center of the screen. An X appears next to the text “dino” beneath it (i.e., not a dinosaur).]

[BUZZER]

we just call them birds today.

[The pterosaur swipes to the left and is replaced by a chicken. Beneath the chicken, a checkmark appears next to the text “dino” (i.e, it is a dinosaur). The chicken is replaced by pigeons, where the checkmark remains and “dino” changes to “dinos”. Danny appears back on screen.]

Many other prehistoric animals often get confused with dinosaurs, like the sail-backed mammal relative Dimetrodon,

[The camera pans over an image of a fossil Dimetrodon.]

as well as fossil mammals themselves, the giant ground sloth or woolly mammoth.

[Camera pans over a giant fossil ground sloth and zooms in on a fossil mammoth.]

People also think sometimes that large marine reptiles, like plesiosaurs, ichthyosaurs, and mosasaurs, are dinosaurs themselves.

[The screen fills with blue, accompanied by the [SOUND OF POURING WATER]. The silhouettes of a plesiosaur, an ichthyosaur, and mosasaur appear, with their names superimposed over their bodies. A giant X appears on top of their silhouettes, next to the word “dino”. They are not dinosaurs.]

You may think that an animal is a dinosaur because it’s large and scaly, but these traits evolved much earlier in evolutionary history.

[The silhouettes for the marine reptiles shrink and are surrounded by names of other large, scaly animals like “Komodo dragon”, “Titanoboa”, “Velociraptor”, and “Dunkelosteus.” Next to these names, the text “Large Scaly Things” appears. Danny appears back on screen over an orange background.]

Just because pterosaurs aren’t dinosaurs doesn’t make them any less amazing. They ruled the skies for over a hundred and fifty million years, and I think that’s really cool.

[Danny is surrounded by full-color illustrations of pterosaurs, and in the background, white silhouettes of pterosaurs fly behind him.]